Improving the dyeing uniformity and thermostability of undrawn acrylonitrile polymer filaments by applying steam under pressure



United States NITRILE POLYMER FELAMENTS BY APPLYING STEAM UNDER PRESSURE James Veith Hewettaild Lawrence Bell Steele, In, Camden, S. C., assignors to E. l. du Pont de Nemours & @ompany, Wilmington, Del., a corporation of Delaware No Drawing. Application March 27, 1953,

7 Serial No. 345,234

4 Claims. (Cl. 3130.1) i

This invention. relates to improving the uniformity of fibers, filaments, yarns and similar articles prepared from acrylonitrile polymers. More particularly, this invention is directed to improving the short length dyeing uniformity and thermostability of continuous filament yarns from such polymers.

Yarn may be produced by an evaporative spinning procedure in which the acrylonitrile polymer is initially in solution. The yarn is Wound up at the spinning machine while it contains 20%, 30%, 40% or more of residual solvent; it is then washed with water or with water containing a small amount of solvent to reduce the residual solvent to below 2.5%. Thereafter, the yarn is drawn from 2 to 10 times or more in a pressure steam drawing cell. Such yarn is frequently characterized by short length dyeing non-uniformities apparently due to more porous or lower density sections which may dye several shades deeper than the main portion of the yarn. Moreover, these yarns, when subjected to treatments at elevated temperatures, occasionally darken severely and non-uniformly.

It is therefore an object of this invention to provide an improved procedure .for processing the spun yarn prior to drawing it to improve dyeing uniformity and to improve thermostability. Other objects will be apparent from the description that follows.

The objects of this invention are accomplished by subjecting the wound package of substantially undrawn yarn, after the solvent has been extractedto reduce the out in an autoclave such as one constructed from a piecev of 8 inch pipe about 6 feet long, supported horizontally and closed at its ends with flanges, one of which may be made easily removable; At the top near one end, a steam inlet pipe is connected through a pressure regulator and at the bottom near the other end a drain connection is located and provided with a steam trap and :a by-pass vent line around the trap. The cakes of yarn can be easily slid into this pipe autoclave with ample roomfor the steam to circulate around the outside of the cakes, through the cake core and between the ends of adjacent cakes. Other apparatus may be used as, for example, autoclaves of other shapes and sizes. A large diameter pressure vessel that permits loading of the cakes ditions for carrying out this invention and are not limitative.

2,768,868 ,Pa'ten'ted Get. 30, 1956 see 2 EXAMPLE I 1,370 denier-80filament yarn produced by dry spinning acrylonitr'ile homopolymer from solution in N,N- dime'thylformamide was wound up outside the spinning cell on to a perforated core about 11 inches long and 3.5 inches outside diameter. The yarn cake itself was about 10 inches long. As collected, the yarn contained about 30% residual solvent and this was reduced to length defects.

about 1.7% solvent by pressure washing with water containing a small amount of solvent and heated to C. When'this yarn without further treatment was drawn in a steam pressure cell to 8 times its undrawn length and thereafter'zheat relaxed, 12%, a yarn of about 200 denier wasflobtained; The drawn yarn rafter twisting to about 0.3 turn per inch was knitted into tubing and dyed with (Delanthrene Pure Blue BRS and numerous short length dyeing; flashes were noted throughout the sample. These-faults were more abundant in the yarn from the outside 10% ,of the original spinning package, and, therefore, this portion of the cake was selected for the comparative tests that follow.

Cakes of washed yarn such as previously described were subjected to steaming in the pipe autoclave described above at the various conditions set forth below and after the cakes were cooled, the yarn was drawn, relaxed and twisted as earlier described in this example. Yarn comprising the outside 10% of the spinning cake was then knitted into tubing, dyed with Celanthrene Pure Blue HRS and then compared with control samples which were similarly prepared except that the yarn was drawn without being subjected to previous steaming. Steaming removes about 90% of the short length dyeing defects and the pressure and time conditions that give this degree of improvement are set forth in the chart below-as well as conditions for a few cases showing less improvement. The time of steaming shown .is from the time the pressure reaches 1 pound per square Percen'mge'slio'rfleng'th defect removal with steam Steaming I .Steaming Time, Minutes Pressure, Pounds/Sq. Gt g In. (Gauge) 5 10 20 30 45 60 90 per perperper; perperper- 1101- per- 42 C6755 cevott cent cent cent cent cent cent cant From these data was developed the empirical formula that follows and subsequent tests on 675 denier-40 filament undrawn yarn as well as additional tests on 1,370

whereP, the absolute pressure in pounds per square inch,

is equal to the gauge pressure plus 14.7 and t is the time in minutes necessary to remove 90% of the short There will, of course, be some minor variations from a constant value, but within the pressure limits previously specified this value will not vary a great deal and the plus or minus 20 (about plus or minus 10%) covers these minor variations i. e., between 168 and 208.

EXAMPLE II A washed package of undrawn 675 denier-4O filament polyacrylonitrile yarn such as described under Example I was subjected to steaming at pounds per square inch gauge pressure for 40 minutes and thereafter was steam drawn and further processed as described under Example I. No dyeing irregularity could be found in the knitted dyed sample whereas a control sample subjected to the same processing steps but unsteamed showed numerous dye flashes. This pressure and time of steaming when substituted in the above formula gives a value of 188.

EXAMPLE III A washed package of undrawn 1,370 denier-80 filament yarn of acrylonitrile/methylacrylate copolymer 94/6 prepared as described under Example I is subjected to steaming at pounds per square inch gauge pressure for 30 minutes and thereafter is steam drawn and further processed as described under Example I. No dyeing irregularity can be found in a knitted dyed sample.

Steam pressures above about 40 pounds per square inch gauge are to be avoided because the time of treatment is so short that good control is impossible and not infrequently the short length dyeing irregularity was found to reverse itself and become a light dyeing streak instead of a dark dyeing streak relative to the bulk of the yarn. Prolonged steaming at pressures below 40 pounds per square inch gauge produces a yarn with poorer drawing continuity and is therefore undesirable. For reasons of control and reproducibility as well as economics, it is preferred that the pressure of steaming be maintained between about 10 and pounds per square inch gauge which means the time of steaming is reasonable, being between about 20 minutes and about 60 minutes.

While the yarn packages are placed in a closed or pressure vessel containing steam, it is to be noted that the yarn is in static contact with the steam. The steam is not forced through the yarn windings. The packages and steam are so related that the steam can get all around the yarn body and steam does get into the body to some extent. If the steam is blown or forced through the package, a light dyeing (reverse) barr is invariably encountered in the final yarn. This adverse efiect is not obtained in the process of this invention. The critical pressures and exposures used in the process of this invention not only produce the uniform dyeing and thermal stability desired, but prevent any adverse effects.

The yarns that are processed by this invention are generally substantially undrawn yarns produced by dryspinning techniques. Some drawing does occur in this and in other methods for producing filaments. While certain drawn yarns can be treated with benefit in accordance with this invention, the process described herein is preferably applied to the as-spun yarns prior to their orientation by stretching. By so doing, rather than applying the process after orientation, the complexity of producing a drawn, void-free yarn is materially reduced and .a yarn that dyes uniformly is attained.

This invention permits production of uniformly dyeable acrylonitrile polymer yarns without adding materially to their cost. While the acrylonitrile homopolymer yarns have been most difiicult to dye uniformly, this invention may also be used to good advantage with yarns of copolymers of acrylonitrile, especially those having a major amount of acrylonitrile. Those acrylonitrile polymers having an acrylonitrile content of about and more are preferred. The copolymers that can be used in this invention are many and are described in such patents as U. S. 2,404,714 to 2,404,727. Steaming in accordance with this invention also reduces thermal discoloration and reduces non-uniformity of discoloration which is highly desirable for uses wherein the yarns, fibers or similar items are bonded under heat and pressure to rubber as is done in the manufacture of automobile decking.

Any departure from the above description which conforms to the present invention is intended to be included within the scope of the claims.

We claim:

1. The process of improving the uniformity of filaments which have not been subjected to a drawing operation and Which contain from 85% to polyacrylonitrile and from 0% to 15% of an acrylate ester copolymerized therewith, which comprises placing the said filaments in an atmosphere of steam under a pressure of from 0 to 40 lbs. per sq. inch gauge for a time between 5 and minutes.

2. The process of claim 1 in which the product of the absolute pressure and the square root of the time in minutes lies between 168 and 208.

3. The process of claim 1 in which the pressure is between 10 and 20 lbs. per square inch gauge.

4. The process of claim 1 in which the time is from 20 to 60 minutes.

. References Cited in the file of this patent UNITED STATES PATENTS Rugeley et al. May 13, 1947 OTHER REFERENCES 

1. THE PROCESS OF IMPROVING THE UNIFORMITY OF FILAMENTS WHICH HAVE NOT BEEN SUBJECTED TO A DRAWING OPERATION AND WHICH CONTAIN FROM 85% TO 100% POLYACRYLONITRILE AND FROM 0% TO 15% OF AN ACRYLATE ESTER COPOLYMERIZED THEREWITH, WHICH COMPRISES PLACING THE SAID FILAMENTS IN AN ATMOSPHERE OF STEAM UNDER A PRESSURE OF FROM 0 TO 40 LBS. PER SQ. INCH GAUGE FOR A TIME BETWEEN 5 AND 150 MINUTES. 